1. Field of the Invention
The present invention relates to an Internet Protocol (IP) key telephone system that allows a terminal unit placed outside a Local Area Network (LAN) within company to be connected to a main unit of the key telephone system.
2. Description of the Related Art
As a telephone system used in a small office, a key telephone system that accommodates a plurality of extension terminal units and switches them with outside lines is known. In addition, an IP key telephone system that uses extension lines of the key telephone system as IP telephone system units through a LAN within company is known. A main unit of the key telephone system accommodates a plurality of IP extension terminal units and switches them with outside lines. In addition, the main unit has a function as an IP server and stores and manages a database of various kinds of information.
However, a terminal unit placed outside the LAN within company cannot access the IP key telephone system and retrieve information from the main unit of the IP key telephone system.